Recently, as an example of a device for reproducing data recorded on an optical disk, there are a compact disk player (hereinafter, referred to as CD player), a CD-ROM drive device in which a compact disk (hereinafter, referred to as CD) is used a read-only memory, etc. As a CD-ROM drive device becomes popular, the request for providing a CD-ROM drive device with a reproducing function which enables fast access while attaining low-power consumption is growing.
Recording systems for a disk include the constant linear velocity system (hereinafter, referred to as CLV system) which is characterized in high-density recording, and the constant angular velocity system (hereinafter, referred to as CAV system) which is characterized in high-speed search. For example, Japanese Patent Unexamined Publication (Tokkai) No. Hei6-36289 discloses a method in which a disk wherein recording was performed by the CLV system is reproduced under CAV-rotation. Japanese Patent Unexamined Publication (Tokkai) No. Sho62-88170 discloses a method in which a disk wherein recording was performed by the CLV system is reproduced at a linear velocity higher than a specified linear velocity. In the former method, influences of the rotation settlement of a spindle servo can be eliminated, and the pickup-moving time is substantially equal to the access time. The latter is a system in which reproduction can be started even in a period when the CLV rotation settlement has not yet reached the final linear velocity. As the rotation number of a spindle motor is increased to a double speed or a quadruple speed, the effects of these systems are further recognized. For example, results of a technical study on the variable linear velocity reproduction system are reported in NIKKEI ELECTRONICS No. 628 (Feb. 13, 1995), pp. 111 to 119. In the report of NIKKEI ELECTRONICS, the term of variable velocity reproduction is used. In the following description, however, reproduction under the state where the linear velocity has not yet reached the final target is called the variable linear velocity reproduction system.
In a usual CD player or a CD-ROM device, the read clock signal is fixed, and the rotation of a disk is synchronized in phase with the read clock signal. Such a player or device is configured so that data which were once stored in a memory or the like by using the write clock signal synchronized with the regenerative clock signal are read out in synchronization with the read clock signal, thereby absorbing the time fluctuation.
By contrast, in a CD-ROM drive device, it is not particularly necessary to read out data by using a fixed clock signal. Therefore, such a device may be configured so as to read out data in accordance with rotation of a disk. The above-mentioned variable linear velocity reproduction system is a reproduction system which was developed in view of the above.